1. Field of the Invention
The present invention relates to a dielectric film and a dielectric element such as a thin-film capacitor which includes the dielectric film.
2. Description of the Related Art
With multi-functionalization of electronic apparatuses, various functions are desired to be added to electronic circuit boards contained in electronic apparatuses. Therefore, the number of electronic components mounted on an electronic circuit board tends to increase. Thus, there is strong demand for improving the mounting density of electronic components.
One of the proposed answers to the demand is to embed electronic components in an electric circuit board. One of the many electronic components mounted on an electronic circuit board is a usual laminated ceramic capacitor. However, when the laminated ceramic capacitor is embedded in an electric circuit board, the thickness of the laminated ceramic capacitor and brittleness due to a ceramic property cause the problem of producing, by the stress generated in an embedding process, cracks in the laminated ceramic capacitor or deformation in a portion of the electric circuit board where the laminated ceramic capacitor is embedded.
It is difficult to resolve the problem even by a usual laminated ceramic capacitor having a very small shape. Therefore, a thinner lower-profile capacitor than the laminated ceramic capacitor is required as a capacitor for embedding in an electric circuit board. A thin-film capacitor is generally known as a low-profile capacitor.
Thin-film capacitors are widely used for decoupling capacitors as small high-performance electronic components. Therefore, thin-film capacitors with high dielectric constant are required.
In the related art, Japanese Unexamined Patent Application Publication No. 10-200069 discloses a technique for a dielectric film including a layer containing columnar crystal grains and a layer containing spherical crystal grains as a dielectric film having a high dielectric constant and high resistivity. Also, for the problem of low reproducibility of Japanese Unexamined Patent Application Publication No. 10-200069, Japanese Unexamined Patent Application Publication No. 11-177051 discloses a technique that a dielectric film includes a layer containing columnar crystal grains and a layer containing spherical crystal grains, and when an oxide of the spherical crystal grains is represented by general formula ABO3, an A element/B element ratio is 1.1 to 1.5. Thus, reproducibility is secured, and improvements in dielectric constant and insulation are realized. However, the dielectric constant is as low as about 450, and thus it is difficult to achieve the currently required capacitance. In addition, no consideration is given to the behaviors of the dielectric constant with direct-current voltage, and no description is made of knowledge about changes in the dielectric constant or capacitance with the structure and direct-current voltage. In general, when a desired capacitance is achieved, a measure often taken is multilayering or more thinning of a dielectric film. In many cases, multilayering cannot be performed because of thicknesses. On the other hand, when thinning of a dielectric film is performed, as an adverse effect, a high voltage is applied to the thinner dielectric film during use, and thus a higher field intensity than usual is applied to the dielectric film. This causes the problem of decreasing the dielectric constant of the dielectric film, resulting in decrease in the capacitance of a dielectric element.